This invention writes to a multi-valve engine and more particularly to an improved air spring arrangement for an engine having at least three valves serving the same cylinder of the engine.
Conventionally, the poppet valves of an internal combustion engine are closed by one or more mechanical springs that are interposed between the stem of the valve and the cylinder head. Normally coil springs are utilized for this purpose. In order to achieve high engine speeds, it has been proposed to use a pair of concentric springs to increase the closing force.
There are several disadvantages to utilizing such mechanical springs. In the first instance, the spring may set up a harmonic action that can cause the valve to not seat properly or appropriately. In addition, the mechanical springs add weight to the engine and both of these features tend to reduce the potential output of the engine by limiting the speed at which the engine can be operated.
Therefore, there have been proposed arrangements that employ an air spring for urging the valves to their closed positions. These air springs generally define a pneumatic chamber that encircles the valve stem and in which a piston is slidably supported and biased by the air pressure in the chamber. This piston is connected to the stem of the valve so that the air pressure will urge the valve to its closed position.
With these arrangements it is the normal practice to employ a pair of air lines and valves that communicate with the pneumatic chambers for supplying air under pressure to them and for controlling the air pressure in the chambers. This obviously requires the formation of appropriate supply and discharge passages in the cylinder head or the member in which the air pressure cylinders are formed.
Although this provision of supply and discharge conduits presents a relatively easily solved problem when utilizing four valve per cylinder cylinder heads, greater problems arise when using a greater number of valves. When four valve per cylinder engines are employed, it is the general practice to have a pair of intake valves on one side of the combustion chamber and a pair of exhaust valves on the other side of the combustion chamber. The respective intake and exhaust valves have their reciprocal axes lying in common planes. This placement permits the use of one drilled passageway that can extend longitudinally through either the cylinder head or the cam carrier, depending upon which member forms the pneumatic cylinders.
Where it is proposed to employ three valves, either for the intake or exhaust valves or both, however, the valve stem axes all do not lie in a common plane. With the use of three valves per cylinder for either the intake or exhaust function, the valve stems are disposed in encircling relationship to the spark plug which is centrally positioned in the combustion chamber. Although the valves may be put in line, then the spark plug must be offset or otherwise disposed so that it will not be in its optimum position.
The use of the varying angular positions for the stems of the three valves also permits the formation of a relatively small combustion chamber having a relatively small surface area that permits high compression ratios and low quenching. With such a valve placement, however, it is then difficult to provide supply passages and discharge passages for delivering and relieving the air from the pneumatic cylinders which are also arrayed in a somewhat circular fashion around the spark plug.
It is, therefore, a principal object of this invention to provide an improved and simplified air spring arrangement for an engine having at least three intake and/or exhaust valves per cylinder.
It is a further object of this invention to provide an improved air spring arrangement for a three valve engine that facilitates the formation of supply and relief passages without interfering with the other components of the cylinder head.
As has been noted, it has been previously the practice to form the air chamber for the air spring in either the cylinder head or in a cam carrier that also journals the camshaft and actuating tappets for the valves. With this arrangement, the formation of the passages and their necessary bores for the pneumatic cylinders can present substantial problems. In addition, the assembly and alignment of all of the components can be difficult.
It is, therefore, a further object of this invention to provide an improved cylinder head assembly for an engine having pneumatically closed valves.
It is a further object of this invention to provide a cylinder head assembly having individual inserts that form at least portions of the pneumatic spring arrangement for closing the valves of the engine, so that the passages therefor can be easily formed and independently of the cylinder head and/or cam carrier.